1,123 research outputs found
Lie-algebraic classification of effective theories with enhanced soft limits
A great deal of effort has recently been invested in developing methods of
calculating scattering amplitudes that bypass the traditional construction
based on Lagrangians and Feynman rules. Motivated by this progress, we
investigate the long-wavelength behavior of scattering amplitudes of massless
scalar particles: Nambu-Goldstone (NG) bosons. The low-energy dynamics of NG
bosons is governed by the underlying spontaneously broken symmetry, which
likewise allows one to bypass the Lagrangian and connect the scaling of the
scattering amplitudes directly to the Lie algebra of the symmetry generators.
We focus on theories with enhanced soft limits, where the scattering amplitudes
scale with a higher power of momentum than expected based on the mere existence
of Adler's zero. Our approach is complementary to that developed recently by
Cheung et al., and in the first step we reproduce their result. That is, as far
as Lorentz-invariant theories with a single physical NG boson are concerned, we
find no other nontrivial theories featuring enhanced soft limits beyond the
already well-known ones: the Galileon and the Dirac-Born-Infeld (DBI) scalar.
Next, we show that in a certain sense, these theories do not admit a nontrivial
generalization to non-Abelian internal symmetries. Namely, for compact internal
symmetry groups, all NG bosons featuring enhanced soft limits necessarily
belong to the center of the group. For noncompact symmetry groups such as the
ISO() group featured by some multi-Galileon theories, these NG bosons then
necessarily belong to an Abelian normal subgroup. The Lie-algebraic consistency
constraints admit two infinite classes of solutions, generalizing the known
multi-Galileon and multi-flavor DBI theories.Comment: 1+48 pages; v2: minor changes and some references added, matches
version published in JHE
Two-loop free energy of three-dimensional antiferromagnets in external magnetic and staggered fields
Using a model-independent low-energy effective field theory, we calculate the
free energy of three-dimensional antiferromagnets in a combination of mutually
perpendicular external magnetic and staggered fields at the
next-to-next-to-leading, two-loop order. Renormalization is carried out
analytically, and the renormalization group invariance of the result is checked
explicitly. The free energy is thus expressed solely in terms of temperature,
the external fields, and a set of low-energy coupling constants, to be
determined by experiment or by matching to the microscopic model of a given
concrete material.Comment: 19 page
Physiological Responses to Acute Silver Exposure in the Freshwater Crayfish (\u3cem\u3eCambarus diogenes diogenes\u3c/em\u3e)—A Model Invertebrate?
Adult crayfish (Cambarus diogenes diogenes) exposed to 8.41 ± 0.17 μg silver/L (19.4% as Ag+) in moderately hard freshwater under flow-through conditions for 96 h exhibited ionoregulatory disturbance, elevated metabolic ammonia (Tamm) production and substantial silver accumulation in the gills, hemolymph, and hepatopancreas. The ionoregulatory disturbance included both a generally reduced unidirectional Na1 influx and an increased unidirectional Na+ efflux, leading to a substantial net loss of Na+ from the silver-exposed crayfish. The Na+ uptake in silver-exposed crayfish differed overall from controls, while the increased Na+ efflux recovered to control values 48 h into the 96 h of exposure. The general inhibition of Na+ uptake could be explained by a reduced sodium/potassium-adenosine triphosphatase (Na/K-ATPase) activity in terminally obtained gill samples from the silver exposed crayfish. The silver-induced effect on Na+ uptake and loss translated to reduced hemolymph Na+ concentrations but not significantly reduced hemolymph Cl- concentrations. Hemolymph Tamm and Tamm efflux both increased in silver-exposed crayfish, indicating an increased metabolic Tamm production. The present study demonstrates that the toxic mechanism of waterborne silver exposure in freshwater crayfish resembles that of freshwater teleost fish. The crayfish might therefore be a useful model system for extending current environmental regulatory strategies, currently based on teleost fish, to invertebrates
Histological and immunohistochemical evaluation of mandibular bone tissue regeneration
The purpose of the study was to perform an immunohistochemical and histological evaluation of samples taken from different bone regeneration procedures in atrophic human mandible. 30 patients (15 men and 15 women, age range of 35-60 years), non-smokers, with good general and oral health were recruited in this study and divided into three groups. The first group included patients who were treated with blood Concentration Growth Factors (bCGF), the second group included patients who were treated with a mixture of bCGF and autologous bone, while the third group of patients was treated with bCGF and tricalcium phosphate/hydroxyapatite (TCP-HA). Six months after the regenerative procedures, all patients undergone implant surgery, and a bone biopsy was carried out in the site of implant insertion. Each sample was histologically and immunohistochemically examined. Histological evaluation showed a complete bone formation for group II, partial ossification for group I, and moderate ossification for group III. Immunohistochemical analysis demonstrated a statistically significant difference between the three groups, and the best clinical result was obtained with a mixture of bCGF and autologous bone
Monolithic zirconia and digital impression: case report
The aim of this study is to present a clinical case of a full arch prosthetic rehabilitation on natural teeth, combining both digital work-flow and monolithic zirconi
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